A wide variety of information systems may include persistent storage devices along with access subsystems for use in accessing the information held on the persistent storage devices. A data center, for example, may include large volumes of disk drives for persistent storage along with information servers for accessing the information contained on the disk drives.
A client of an information system may access the information system by generating access transactions that target the information stored on the persistent storage devices of the information system. Examples of access transactions include SQL read/write/modify transactions.
An access subsystem may function as a cache of information contained in persistent storage. For example, the main memories in the information servers in a data center may be used as a cache of information contained on the data center disk drives. The caching of information may improve response time when handling access transactions.
An information system having multiple access subsystems may include a mechanism for assigning the incoming access transactions received from clients to individual access subsystems. For example, a data center may include a transaction router that assigns incoming access transactions to individual information servers in a round-robin fashion.
It is often desirable to reduce the power consumption of an information system. In a data center, for example, it may be desirable to reduce power consumption during low use periods in order to reduce the costs of operating the data center. In addition, it may be desirable to reduce the power consumption to reduce heat in the data center environment. A reduction in heat in a data center may increase the reliability of hardware in a data center and may enable more density in data center hardware.
The power consumption in an information system may be reduced by switching off individual access subsystems. In a data center, for example, power consumption may be reduced by switching off individual information servers during low use periods. Unfortunately, the switching off of access subsystems in a prior information systems that assign incoming access transactions to access subsystems in a round-robin fashion may cause the loss of valuable cached data and slow the overall response time in an information system.